The present invention relates to a device for measuring the effective porosity of a sample.
It is frequently desired to measure the porosity of a portion of a package, and particularly sterile packages. The reasons for desiring to determine the porosity of the package include the following: (1) to determine whether the package provides a sterile barrier, (2) to determine whether the package can be sterilized by gas, and (3) to determine the package integrity. Thus, porosity is an important attribute of most medical packages, especially those which contain products which are gas sterilized. In addition to product containment and protection, a package must be able to maintain sterile integrity during normal shipment, storage, and sterilization. Excessively low porosity materials may present good barrier properties, but not be able to withstand normal sterilization pressure changes without package failure. Excessively high porosity materials may withstand pressure changes well, but not be a sterile barrier.
The presently accepted manner of measuring porosity is with a Gurley Densimeter which measures the time necessary for 100 cc of air to pass through one square inch of sample area with a constant pressure of 4.88 inches of water. Results are reported in Gurley Seconds which are the inverse of porosity (i.e. the higher the Gurley Seconds, the lower the porosity). This method is hampered by the small area measured and inherent possibility of contaminating the test sample with oil by the device. A second instrument is the ARO porosity tester which measures porosity in Gurley Seconds using a calibrated pressure of 4.88 inches of water. While this unit does not exhibit the oil contamination potential, it still measures only one square inch of sample (10 square inch attachment is available, but requires multiplication of results to obtain Gurley Seconds), and is prone to mechanical problems which are not always obvious when conducting a test. Problems have been experienced when trying to obtain agreement or correlation between different pieces of test equipment on the same test sample.